1. Field of the Invention
The present invention relates to a cross-point semiconductor memory device and a method of manufacturing the same.
2. Description of the Related Art
A most common semiconductor nonvolatile memory is a flash memory, and a NOR flash memory or a NAND flash memory is widely used for code storage or data storage. In recent years, a new nonvolatile memory, for example, a resistance-change memory including a phase-change memory (Phase change RAM, PRAM) is suggested as an alternative to a flash memory. This nonvolatile memory has a structure in which a memory part is arranged between upper and lower electrodes, so it has a simple memory structure and can be easily miniaturized. A phase-change memory that is one of a resistance-change memory is a nonvolatile memory in which a phase-change material for a memory part whose electrical resistance varies between an amorphous state and a crystalline state by several digits is used for an operation as a memory (for example, see JP-A-2007-134676). As a type of resistance-change memory, a nonvolatile memory is suggested in which data is stored by a colossal magneto-resistance effect (CMR effect) of a storage material forming a memory part (for example, see JP-A-2003-068983). Alternatively, as a type of resistance-change memory, a nonvolatile memory is suggested in which a memory part is made of an ion conductor containing a metal (for example, JP-A-2005-166976 or JP-A-2005-197634). In addition, as a type of resistance-change memory, a PMC (Programmable Metallization Cell) is suggested (for example, see JP-A-2005-322942).
With regard to these nonvolatile memories, there is an effort to increase integration, and studies are being conducted for a so-called cross-point semiconductor memory device. The cross-point semiconductor memory device includes bit lines, word lines, and memory parts arranged at intersections (cross-points, overlap areas) between the bit lines and the words lines, and made of a storage material for storing data. Then, data stored in a memory cell positioned at an intersection between the selected bit and word lines is directly read without using a selection transistor. The cross-point semiconductor memory device has a simple structure, so in terms of achievement of high capacity, the cross-point semiconductor memory device is attracting attention. As the memory part constituting the cross-point semiconductor memory device, the above-described resistance-change memory is suggested.
FIG. 26 shows an arrangement example of word lines, bit lines, and memory parts in a cross-point semiconductor memory device. The word lines and the bit lines are arranged in a line-and-stripe shape in a direction in which the projection images thereof are orthogonal to each other. The minimum size of one memory cell including a word line, a bit line, and a memory part arranged at an intersection between the word and bit lines is 4F2. “F” means a minimum process dimension defined by the design rule of a manufacturing process for manufacturing a cross-point semiconductor memory device (a minimum line width dimension and a minimum interval dimension under the restriction of the manufacturing process). The minimum process dimension F is a dimension that is usually restricted by resolution ability of photolithography. That is, the minimum value of the width of the bit line or word line and the wiring interval is “F”, so the minimum size of the memory cell is 4F2.